WASHINGTON (Reuters) - Vice President Joe Biden, already deeply immersed in high-profile domestic policy, is finding that his clout extends to foreign affairs as well, as he plays a top surrogate role for President Barack Obama in the early days of their second term.

Biden is now in many ways viewed as Obama's "Mr. Fix-it," who struck a crucial budget deal in January and who is able to navigate his way comfortably through Washington's complex power structure with a back-slapping joviality that Democrats find endearing despite the occasional verbal misstep.

The 70-year-old former senator has often been viewed as gaffe-prone, which makes his wide influence all the more remarkable. Just last year Biden was the subject of media speculation that Obama, when his re-election campaign was struggling, might dump him in favor of Hillary Clinton.

"I think what's striking about Biden's role, particularly recently, is both the public nature of it and the significance of the portfolios," said Joel Goldstein, an expert on the vice presidency at St. Louis University.

A Reuters-Ipsos poll last week showed Biden leading several of the Republicans most often mentioned as potential 2016 contenders, like former Florida Governor Jeb Bush and New Jersey Governor Chris Christie.

"In terms of how Biden is perceived, there's a real sort of folksiness - for lack of a better term - that people find appealing," said Ipsos pollster Julia Clark. "He puts his foot in his mouth, but who doesn't? It's sort of what makes him more relatable."

Obama, who has maintained a tight control of foreign policy out of the White House, sent his No. 2 to Munich this month to hold his second administration's first face-to-face contacts with key U.S. allies. Biden visited France and Britain as well as Germany.

In Munich, Biden dangled the possibility of direct U.S. talks with Iran over its nuclear ambitions, which would be a departure from the typical U.S. pattern of dealing with Tehran along with five other major powers.

And under pressure to do more to help Syrian rebels, Obama had Biden meet with Syrian opposition leaders and assure them the United States would send them humanitarian aid in their bid to oust the Syrian government.

Such a high-profile role contrasts with the way many past vice presidents have been relegated to ceremonial functions like representing the United States at funerals abroad.

Some vice presidents, like Dick Cheney under George W. Bush, played powerful roles, but behind the scenes.

Biden has played significant roles both publicly and privately, working internally as a sort of contrarian to challenge policies on Iraq and Afghanistan, for example, while publicly taking on difficult sales jobs, like promoting Obama's unpopular $787 billion economic stimulus plan in the first term.

As a devout Catholic, Biden's public support for gay marriage last year caught the White House off guard and forced Obama to voice his own backing for same-sex marriage.

"It's been that way from the beginning," said Aaron David Miller, an expert at the Woodrow Wilson Center. "You can't diminish Biden's role over the first four years. He's been incredibly public and very active."

OPPOSITES ATTRACT?

In many ways, Biden is the exact opposite of the calm, cool and unflappable Obama, being more prone to bombast and show boating.

So it comes as no surprise that the satirical website, The Onion, has developed an comedy series about him. The Onion's Biden is a boozer - the real Biden does not drink - who stole "800 feet of copper wire from a foreclosed home" and washes a Trans Am muscle car in the White House driveway, shirtless.

Sometimes there is a sense that the fake Biden of The Onion and the real one are somehow linked - such as when he was on Capitol Hill to swear in senators.

He told attendees at the Munich security conference that he had traveled over 640,000 miles (1.02 million km) since becoming vice president, and added: "Most the time the president sends me to places that he doesn't want to go!"

Biden's loose tongue may have led Americans to underestimate his role in Obama's first term.

But recent events, such the fiscal-cliff crisis, have shown how reliant the president is on him.

It was Biden who brought about escape from fiscal chaos late last year by finding common ground with Senate Republican leader Mitch McConnell, whose antipathy for Obama is such that he once vowed his major goal was to deny him a second term.

And it was Biden who negotiated with various groups and came up with the first U.S. gun-control proposals in decades, recommendations that Obama quickly endorsed and Congress is now discussing.

Just last week Biden was on Capitol Hill taking the temperature of Senate Democrats on the gun control proposals. Having spent 30 years in the Senate, he is viewed on Capitol Hill as a more credible voice than Obama, who served less than a full term as a senator.

"Senator Obama was here for 30 minutes; Senator Biden was here for 30 years. That's the biggest difference. He's a lot less cocky, doesn't hog the conversation, let's everybody speak, and he understands it," said an aide to a senior Republican senator.

Inevitably, conversation about Biden turns to whether he will seek the Democratic presidential nomination in 2016. He has not ruled this out.

Biden fueled speculation about his plans by staging a party of long-time friends and associates at his home in last January to celebrate his second swearing-in. It included guests from the early voting states of Iowa and New Hampshire.

Biden will have to decide whether he can get elected at 74, an advanced age for a president, and whether he would want to run against former Secretary of State Hillary Clinton, should the 65-year-old wife for former President Bill Clinton decide to stand as well.

At the White House, officials are well aware of the speculation and want Biden to be a successful vice president should he decide to seek the top job. And the best way for him to be a successful vice president, they say, is for Obama to be a successful president.

At the same time, Obama and the White House have been careful not to choose sides between Biden and Clinton.

White House spokesman Jay Carney skirted the issue when asked if Obama preferred one or the other.

"I think for the sake and sanity of all involved, it's worth taking a little bit of a break from presidential election-year politics," he said.

(Reporting By Steve Holland; Editing by Fred Barbash, Mary Milliken and David Brunnstrom)